Edge WASM

A WebImage artifact with backend = "wasm-lm" compiles Java or Kotlin to WebAssembly for JavaScript hosts that compile WebAssembly at runtime. The module keeps its heap and garbage collector in linear memory, so the host needs no WasmGC support. Like the browser build, it starts through its JavaScript loader; it is not a WASI module or component, and it does not deploy to Cloudflare Workers.

Build

Prerequisites match the browser build: Binaryen’s wasm-as on PATH, and code that meets the Native Image requirements.

amends "elide:project.pkl"
import "elide:Jvm.pkl" as jvm
import "elide:NativeImage.pkl" as nativeImage

name = "hello-edge"

artifacts {
  ["app-jar"] = new jvm.Jar {
    sources { "main" }
  }
  ["edge"] = new nativeImage.WebImage {
    from { "app-jar" }
    name = "hello"
    entrypoint = "Hello"
    backend = "wasm-lm"
    runtime = "node"
  }
}

elide build
node .dev/artifacts/native-image/hello.js

Without a manifest:

elide javac -- -d classes Hello.java
elide native-image -- --tool:wasm-lm -cp classes -o hello Hello

Property	Edge value
`backend`	`"wasm-lm"`.
`runtime`	`"node"` for Node-compatible APIs; `"generic"` also detects browser APIs.
`autoRun`	`true` (default) runs `main` when `hello.js` loads.

Output and size

File	Deploy	Hello-world size
`hello.js`	Yes: the loader.	42 KB
`hello.js.wasm`	Yes: the module.	2.1 MB (660 KB gzipped)
`hello.js.wat`	No: text form, for inspection.	38 MB
`hello.js.map`	Optional: emitted with `sourceMap = true`.

A linear-memory module is larger than the WasmGC build of the same program, which uses the host’s garbage collector.

Host requirements

Requirement	Reason
WebAssembly exception handling with `exnref`	The module uses it.
Compiling WebAssembly from bytes at runtime	The loader reads `hello.js.wasm` and compiles it on start.
Node `fs` or `fetch`	The loader reads the module through one of them.

Host	Runs the bundle
Node.js 25+	Yes: `node hello.js`.
Bun	Yes: `bun hello.js`.
Cloudflare Workers	No: Workers compile only modules bundled at deploy time and reject the loader’s runtime compile with `Wasm code generation disallowed by embedder`.
WASI hosts (Fastly Compute, Wasmtime)	No: the module imports from its JavaScript loader, not WASI.